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The Chézy Formula is a semi-empirical resistance equation [1] [2] which estimates mean flow velocity in open channel conduits. [3] The relationship was conceptualized and developed in 1768 by French physicist and engineer Antoine de Chézy (1718–1798) while designing Paris's water canal system.
The Chézy equation is a pioneering formula in the field of fluid mechanics, and was expanded and modified by Irish engineer Robert Manning in 1889 [1] as the Manning formula. The Chézy formula concerns the velocity of water flowing through conduits and is widely celebrated for its use in open channel flow calculations. [ 2 ]
Thus the water discharge of a tap (faucet) can be measured with a measuring jug and a stopwatch. Here the discharge might be 1 litre per 15 seconds, equivalent to 67 ml/second or 4 litres/minute. This is an average measure. For measuring the discharge of a river we need a different method and the most common is the 'area-velocity' method.
The discharge is constant throughout the reach of the channel under consideration. This is often the case with a steady flow. This flow is considered continuous and therefore can be described using the continuity equation for continuous steady flow. Spatially-varied flow. The discharge of a steady flow is non-uniform along a channel.
The discharge formula, Q = A V, can be used to rewrite Gauckler–Manning's equation by substitution for V. Solving for Q then allows an estimate of the volumetric flow rate (discharge) without knowing the limiting or actual flow velocity. The formula can be obtained by use of dimensional analysis.
It is described by the fact that the discharge through a river of an approximate rectangular cross-section must, through conservation of mass, equal Q = u ¯ b h {\displaystyle Q={\bar {u}}bh} where Q {\displaystyle Q} is the volumetric discharge, u ¯ {\displaystyle {\bar {u}}} is the mean flow velocity, b {\displaystyle b} is the channel ...
The wall shear stress τ is dependent on the flow velocity u, they can be related by using e.g. the Darcy–Weisbach equation, Manning formula or Chézy formula. Further, equation ( 1 ) is the continuity equation , expressing conservation of water volume for this incompressible homogeneous fluid.
In civil engineering practice, the Manning formula is more widely used than Stricker’s dimensionally homogeneous form of the equation. However, Strickler’s observations on the influence of surface roughness and the concept of relative roughness are common features of a variety of formulas used to estimate hydraulic roughness. [1] [4]